How to calculate the total working hours of an employee from a set or records?

I have a table named timetable. it contains id,in_time,out_time.

id varchar(20)
att_date date
in_time timestamp
out_time timestamp

the sample details are

id date in_time out_time
C001 2009-10-31 2009-10-31 11:30:00 2009-10-31 12:00:00
C001 2009-10-31 2009-10-31 12:30:00 2009-10-31 1:00:00
C001 2009-10-31 2009-10-31 1:30:00 2009-10-31 2:00:00
C001 2009-10-31 2009-10-31 2:30:00 2009-10-31 3:00:00
C001 2009-10-31 2009-10-31 3:30:00 2009-10-31 5:00:00

i want the employee total working hours:minutes:seconds for a given date. for example for 2009-10-31 the employee working hours is 02:30:00.

please help me with this. thank you all in advance.